Method for controlling an automatic gearbox according to a road profile

ABSTRACT

A method for automatically controlling the gearbox of a road vehicle uses a computer using information on displacement speed and transversal acceleration of the vehicle and engine load in order to apply various shifting rules according to the road profile. The gearbox computer applies different gear shifting rules according to the value of a coefficient of activity Kbend depending on the displacement speed of the vehicle (V), the lateral acceleration of the vehicle (Gt) and the derivative thereof in relation to time (dGt/dt).

The present invention pertains to the control of automatic orstepped-ratio automated transmissions.

More precisely, it relates to a method of controlling a road vehicleautomatic transmission by computer utilizing the information regardingspeed of travel and transverse acceleration of the vehicle and engineload, so as to apply various road profile dependent shift laws to thetransmission.

This invention applies equally well to the control of transmissions ofthe automatic gearbox type comprising one or more epicyclic gear trainsassociated with several brakes or clutches placed under the supervisionof an electronic computer, as to the control of transmissions of thetype comprising an assembly of sliding gears and synchromeshes withrobotized control, or of the continuously variable transmission type.

It is based on utilizing the level of the vehicle's lateralacceleration, measured or estimated while cornering, to determine acriterion making it possible to evaluate the type of road profile (bendyor otherwise), doing so in order to impose various shift laws for thegears (or “variograms” in the case of a continuously variabletransmission) on for example the computer of an automatic transmission,these laws then being suitable for the bendy profile of said road.

Several solutions are known for imposing various shift laws, as afunction for example of the driver's style of driving, of the profile ofthe road (rising and falling). These solutions do not enable automatictransmissions to be suitably adapted when the road becomes bendy.Specifically, over such stretches, it would be desirable to adopt a setof shift laws making it possible to keep spare torque for the wheel (byincreasing for example the engine revs), so as to aid pick-ups aftereach cornering, and thus avoid phenomena of ratio hunting (or ofvariations in ratio in the case of continuously variable transmissions)and which detract from the pleasure of driving the vehicle on bendyroads.

The invention aims to remedy the drawbacks of the known systems forallowing for the profile of the road.

With this objective, it proposes that the computer of the transmissionapply various shift laws for the ratios according to the value of anactivity coefficient Kcorner dependent on the speed of travel of thevehicle (V), on the lateral acceleration of the vehicle (Gt) and on itsderivative with respect to time (dGt/dt).

If the transmission has stepped ratios, the computer applies variousdiscrete change of ratio laws.

If on the other hand it is a continuously variable or infinitelyvariable transmission, it applies various continuous change of ratiovariograms.

Preferably, the activity coefficient Kcorner is obtained from theproduct of the transverse acceleration (Gt) and its derivative withrespect to time (dGt/dt).

The lateral acceleration of the vehicle can be determined either from anacceleration sensor, or according to a reconstruction procedure based oninformation representative of the angle of rotation of the steeringwheel or else on information representative of the speed of the wheels,such as described in French Patent application No. 99-15865 as yetunpublished.

Other characteristics and advantages of the invention will becomeclearly apparent on reading the following description of a particularembodiment thereof while referring to the appended drawings, in which:

FIG. 1 diagrammatically represents the method according to theinvention,

FIG. 2 brings together in a functional diagram, the main steps of theproposed strategy for determining the bendiness factor of the roadKcorner

FIG. 3 brings together in a functional diagram, the proposed strategyfor determining the transmission ratio suited to the bendiness of theroad.

The various items of information regarding vehicle speed (V) andtransverse acceleration (Gt) which are mentioned in FIG. 1 are utilizedin accordance with the invention by a specific unit 100 which determinesa bendiness coefficient Kcorner. The latter then feeds the block 101which also receives other information representative of the forwardspeed of the vehicle V and of the is engine load “load_engine” which mayby way of nonlimiting indication be the angle of opening of the throttlevalve or the accelerator pedal, or else a power or a torque delivered bysaid engine. This block 101 determines the transmission ratio “ratio” tobe applied to the transmission represented by the block 102; thisdetermination is performed according to the method described in theinvention, by selecting a set of shift laws (in the case ofstepped-ratio transmissions) or of a “variogram” (in the case ofcontinuous-ratio transmissions), which is dependent on Kcorner.

On the basis of the transverse acceleration “Gt”, the block 201determines the filtered derivative “dGt/dt” of the transverseacceleration (cf. FIG. 2), then the product of “Gt” and “dGt/dt”. Thisproduct is corrected according to the forward speed of the vehicle inthe block 202. The result of this operation is then filtered in theblock 203 which ultimately determines the coefficient Kcorner. Thisdetermination of Kcorner makes it possible, when cornering, to weightthe cornering dynamics of the vehicle by the level of transverseacceleration which is achieved and also according to the speed of thevehicle; thus, a driver who drives relatively sportily on a bendy roadwill have a high coefficient Kcorner, and which is weighted according tothe speed of the vehicle so as to avoid overly frequent detectionsduring urban type driving or on freeways at sustained speed.

The block 301 (cf. FIG. 3) determines on the basis of the bendinesscoefficient Kcorner a set of gear change laws (or “variogram” in thecase of a continuous ratio transmission). By way of nonlimiting example,when Kcorner is greater than a specified threshold, a set of gear changelaws which is suited to the fact that the road is regarded as bendy isadopted. This set of shift laws makes it possible to increase the sparemotive power (favouring in particular the lower ratios), doing so inorder to aid the pick-up of the vehicle when coming out of the corner.When Kcorner is below the specified threshold, a set of gear change lawswhich is suited to the “normal” driving conditions, that is to saysuited to a road requiring little cornering is adopted.

The block 302 determines in a conventional manner the transmission ratioto be applied to the transmission, from the information representativeof the forward speed of the vehicle (V) and of the engine load which mayby way of nonlimiting indication be the angle of opening of the throttlevalve or the accelerator pedal, or again a power or a torque deliveredby said engine.

1. A method of controlling a road vehicle automatic transmission bycomputer utilizing the information regarding speed of travel andtransverse acceleration of the vehicle and engine load, so as to applyvarious road profile dependent shift laws to the transmission,characterized in that the computer of the transmission applies variousshift laws for the ratios according to the value of an activitycoefficient Kcorner dependent on the speed of travel of the vehicle (V),on the lateral acceleration of the vehicle (Gt) and on its derivativewith respect to time (dGt/dt).
 2. The method of control as claimed inclaim 1, characterized in that the computer applies various discretechange of ratio laws.
 3. The method of control as claimed in claim 1,characterized in that the computer applies various continuous change ofratio variograms.
 4. The method of control as claimed in claim 1,characterized in that the activity coefficient Kcorner is obtained fromthe product of the transverse acceleration (Gt) and its derivative withrespect to time (dGt/dt).
 5. The method of control as claimed in claim4, characterized in that the product of the transverse acceleration (Gt)and its derivative with respect to time (dGt/dt) is weighted by thespeed of travel of the vehicle.
 6. The method of control as claimed inclaim 1, characterized in that the computer adopts a set of shift lawswhich is suitable for roads which are not very bendy when the activitycoefficient Kcorner is below a specified threshold.
 7. The method ofcontrol as claimed in claim 1, characterized in that the informationregarding engine load is given by the opening of the engine throttlevalve.
 8. The method of control as claimed in claim 1, characterized inthat the information regarding engine load is given by the position ofthe accelerator pedal.
 9. The method of control as claimed in claim 1,characterized in that the information regarding engine load is given bya measurement of the power provided by the engine.
 10. The method ofcontrol as claimed in claim 1, characterized in that the informationregarding engine load is given by a measurement of the torque deliveredby the engine.
 11. The method of control as claimed in claim 2,characterized in that the activity coefficient Kcorner is obtained fromthe product of the transverse acceleration (Gt) and its derivative withrespect to time (dGt/dt).
 12. The method of control as claimed in claim3, characterized in that the activity coefficient Kcorner is obtainedfrom the product of the transverse acceleration (Gt) and its derivativewith respect to time (dGt/dt).
 13. The method of control as claimed inclaim 2, characterized in that the computer adopts a set of shift lawswhich is suitable for roads which are not very bendy when the activitycoefficient Kcorner is below a specified threshold.
 14. The method ofcontrol as claimed in claim 3, characterized in that the computer adoptsa set of shift laws which is suitable for roads which are not very bendywhen the activity coefficient Kcorner is below a specified threshold.15. The method of control as claimed in claim 4, characterized in thatthe computer adopts a set of shift laws which is suitable for roadswhich are not very bendy when the activity coefficient Kcorner is belowa specified threshold.
 16. The method of control as claimed in claim 5,characterized in that the computer adopts a set of shift laws which issuitable for roads which are not very bendy when the activitycoefficient Kcorner is below a specified threshold.
 17. The method ofcontrol as claimed in claim 2, characterized in that the informationregarding engine load is given by the opening of the engine throttlevalve.
 18. The method of control as claimed in claim 3, characterized inthat the information regarding engine load is given by the opening ofthe engine throttle valve.
 19. The method of control as claimed in claim4, characterized in that the information regarding engine load is givenby the opening of the engine throttle valve.
 20. The method of controlas claimed in claim 5, characterized in that the information regardingengine load is given by the opening of the engine throttle valve.